1. Field of the Invention
The present invention relates to a technique on an optical scan device or an image display device which includes an optical scanner having a reflection mirror capable of reflecting incident light and performs optical scanning by changing an angle made by the reflection mirror and an incident direction of the incident light, and more particularly to a method of changing a resonance frequency of the optical scanner, and a method of correcting a position of the reflection mirror and the like.
2. Description of the Related Art
As an optical scanner which scans light, there has been already known an optical scanner which includes a reflection mirror for reflecting incident light and performs scanning of reflection light from a reflection surface of the reflection mirror by changing an angle of the reflection surface, that is, an angle made by the reflection surface of the reflection mirror and an incident direction of the incident light.
This type of optical scanner has been used in the field of image formation and the field of image reading, for example. In the field of image formation, the optical scanner is used in applications such as a retina-scanning-type display device which directly scans a luminous flux and directly displays an image on a retina, a projector, a laser printer and laser lithography. On the other hand, in the field of image reading, the optical scanner is used in applications such as a facsimile, a copier, an image scanner and a bar-code reader.
Here, as a method of scanning reflection light using such an optical scanner, there has been known a method which scans the reflection light by oscillating a reflection surface of a reflection mirror. Here, the reflection surface is oscillated by oscillating a resiliently deformable portion which is connected to the reflection surface at a resonance frequency.
However, such an optical scanner makes use of resonance oscillations and hence, the optical scanner is highly dependent on resonance characteristic. Since the resonance characteristic possesses temperature dependency, when an ambient temperature is changed, the resonance frequency of the optical scanner is changed. Further, when the optical scanner is oscillated and a temperature of a resiliently deformable portion is elevated due to heat generated in the inside of the optical scanner, the resonance frequency is changed in the same manner. Further, due to irregularities in characteristics among the respective optical scanners which occur at the time of manufacturing the optical scanner, the resonance frequency may be deviated from a targeted resonance frequency.
When the resonance frequency is deviated from the targeted resonance frequency in this manner, oscillation amplitude of the resiliently deformable portion, that is, a scanning angle becomes small and hence, it is not possible to obtain a desired scanning angle. Accordingly, there has been proposed an optical scanner which feedbacks a signal having a magnitude corresponding to oscillation amplitude of a reflection mirror and allows the reflection mirror to perform the self oscillations at a resonance frequency for acquiring the maximum oscillation amplitude (see JP-A-7-181415 (patent document 1), for example). Further, there has been also proposed an optical scanner which can adjust a resonance frequency of a resiliently deformable portion which is connected to a reflection surface of a reflection mirror. In this optical scanner, a piezoelectric element is formed on the resiliently deformable portion. By applying a voltage to the piezoelectric element, a width, a thickness or a length of the resiliently deformable portion is changed and hence, a spring constant of the resiliently deformable portion is changed whereby the resonance frequency of the resiliently deformable portion can be adjusted (see Japanese Patent No. 2981600 (patent document 2), for example).